Pipette



y 1957 ,s. M. BROADWIN 2,798,647

PIPETTE Filed May 11, 1954 1N VEN TOR. (Yd/V051 M EROAOlV/IV United Sttes PIPETTE Application May 11, 1954, Serial No. 428,935

6 Claims. or. 222-309 This invention relates to pipette instruments for measuring liquid volumes and for receiving and dispensing a predetermined volume of liquid therefrom, said instru ments being preferably employed for titration and other laboratory work.

It is an object of this invention to provide means afiording adjustment of the volume of liquid received or dispensed from a pipette.

A further object of the present invention is to provide means assuring satisfactory measured receipt and discharge of a liquid from a pipette.

Yet another object of the present invention is to provide means facilitating repeated and successive discharge of a predetermined volume of liquid from a pipette following a single initial calibration operation.

Another object of the present invention is to provide means conducive to a portable structure including a liquid supply reservoir and pipette means connected thereto for repeatedly dispensing predetermined as well as varying volumes of liquid therefrom.

These and other objects may be realized by the present invention, described in the accompanying drawing, in which:

Fig. 1 is a side elevational view of a pipette made in accordance with the'present invention;

Fig. 2 is a longitudinal sectional view of the pipette of Fig. l;

' Fig. 3 is a top plan view of the pipette of Fig. 2;

Fig. 4 is a somewhat enlarged sectional view taken along lines 4-4 of Fig. 2; and

Fig. 5 is a side elevational view of the pipette of Fig. 1, drawn to a reduced scale, in combination with a liquid supply reservoir with a common support therefor.

Referring now more particularly to Fig. 2, there is disclosed a tubular member 11 made from transparent material, such as glass or plastic composition, and having a reduced open end 12 at the bottom thereof. The upper end of member 11 is provided with a lip 13 extending exteriorly thereof. Graduations 14 (Fig. l) are provided on the outer face of member 11 representing conventional volumetric units, e. g., fluid ounces, cubic centimeters, or the like. i t

A T-shaped fitting 15 is connected at opening 16 to the member 11 about reduced end 12. The fitting 15 is provided with a branch 17 which is normally sealed oil. from the longitudinal channel 18 of the fitting 15 by a oneway, spring-urged suction valve 19 so that liquid may enter channel 18 through branch 17 but may not pass out therethrough. Abutments 20 extend into channel 18 and provide a seat for a one-way, spring-urged discharge valve 21, which permits liquid to flow out through tapered nozzle 22, but does not permit backflow of liquid.

A piston 23 extends into member 11 and is provided with an enlarged end 24. Collar or first element 25 encircles piston 23 adjacent enlarged end 24 and is provided with a friction ring 26 directly contacting the piston and secured thereagainst by screw 27 (Figs. 1 and 3). Base ring or second element 28 surrounds member 11 and Inc, New Yorl;,

2 is connected with collar 25 by frame 29, comprising rods 30 and pins 31.

A first member forming an abutment or upper locking ring 32, is composed of friction material and is retained against member .11 by set screw 33. Said abutment ring is disposed in the embodiment shown intermediate.

base ring 28 and lip 13. A second member forming lower locking ring 34 encircles the member 11 below base ring 28. This lower locking ring 34 includes set screw 35 acting against friction element 36 to thereby secure the locking ring 34 exteriorly to the member. Laterally pro jecting finger stalls 37 are provided on lower locking ring 34 as a support during manipulation of the pipette.

Sleeve 38 extends upwardly toward base ring 28 and is spaced from-the member 11 providing a shoulder 39 at the base of a recess 40.

Helical spring 41 loosely surrounds the member 11, abutting against slidable base ring 28 and fixed shoulder 39 forming a seat for said spring in recess 40.

In Fig. 5, the pipette is supported by bracket 42 attached to upright 43 which in turn is connected to base 44.

In operation, the pipette is grasped by two fingers of an operators hand at finger stalls 37 and pressed with the thumb against enlarged end 24 of the piston. On

moving the fingers towards each other against the action of spring 41, base ring 28 together with frame 29, collar 25 and piston 23 are advanced downwardly to the posi' tion shown in dotted lines in Fig. 1. In this position, the piston empties the member 11 of any liquid or air contained therein through discharge valve 21. p p On releasing the finger stalls 37, the compression of spring 41 returns the piston to the position shown in Fig. 2. Since this tends to reduce the pressure within member 11 due to the one-way action of discharge valve 21, liquid from reservoir 46 flows into the member through suction valve 19. On again grasping finger stalls 37 and working against the action of spring 41, the liquid contained in member 11 will be dispensed through; discharge valve 21 while one-way suction valve 19 seals off branch 17. By intermittently grasping the finger stalls 37, depressing the piston by working against spring-41 and releasing the finger stalls, successive quantities of liquid of predetermined and equal volume will be discharged first from the liquid supply reservoir 46 and then in turn from nozzle 22.

By the novel arrangement herein described, since the piston terminates its travel at a point substantially above suction valve 19 and discharge valve 21, a cushion of liquid will always remain within fitting 15 to prevent said valves from damage due to a sudden increase or decrease of pressure, thereby protecting said valves from damage and lengthening the useful life of the apparatus. Upon completion of operation if it is desired to exhaust all the liquid within the pipette this can be efiected by severing the connection between branch 17 and the liquid supply reservoir so that the branch 17 is in communication with the atmosphere. Upon working the piston, air will be sucked into the pipette and during the discharge phase The locking rings 32 and 34 are adjustably retained against the member 11 by screws 33 and 35, respectively Patented July 9, 1957.

varied .so thatthe volume of liquid sucked in and discharged in each cycle may be similarly varied.

This resetting of the locking rings will simultaneously serve, tochange the tension on the spring .41 so that the rate of return of the piston to its initial position of rest may be-selected at will in accordance with the characteristics, e. g. viscosity of the liquid being dispensed.

. The locking rings-may be so positioned on the member 11 that the pistion in itstravel will not reach the reduced end 12 but rather will be prevented from further movement, i. e. limited, by abutment of base ring 28 against lower locking ring 34 so that, any pressures which the member will have to withstand will be applied longitudinally along the wall rather than perpendicularly to the base of the member which is relatively weaker, thereby ensuring continued satisfactory operation free from failure and avoiding the necessity for interruption to replace damaged or broken members.

Moreover, the distance between the locking rings may bemaintained at a fixed value while nonetheless the lowermost point of travel of the piston within the member 11 may be spaced from reduced end 12 by adjustment of collar 25. Consequently, the extent of piston travel as well as the lowermost point of travel of the piston and the amount of tension on the spring may all be fixed independently of each other.

In assembling the novel pipette, the spring 41 may be positioned between the base ring 28 and upper locking ring 32. In such an arrangement the base ring 28 would normally rest against the lower locking ring 34 with the piston in the discharge position. By changing the disposition of the spring relative to the base ring, therefore, the normal state of the pipette may be changed at will from oneof receivingliquid or one of discharging liquid.

As a further alternate, the finger stalls 37 may be positioned on the upper locking ring to decrease the distance to be spanned by the fingers of the operator in working the pipette. In place of a transparent tubular member, one made of translucent material may be employed. For ruggedness, the member 11 may even be composed of metal'sincethe volume of liquid dispensed depends upon the distance between'the locking rings which can be determined by the external graduations on the member.

The system as shown in its entirety in Fig. is particularly useful in exacting laboratory work since liquid may be supplied from reservoir 46 to any receptacle placed beneath nozzle 22 without direct contact or opportunity for spilling.

Such an arrangement is especially useful in titrations wherein several specimens and a control must all be supplied With the same amount of reagent after which a backtitration with a standard solution is effected, as in saponifications, hydrolyses, and the like. With the novel pipette by suitable initial adjustment of the locking rings or collar the apparatus can be set to deliver a desired amount of liquid in each cycle. Thereafter, only an intermittent movement of the piston is necessary to discharge equal volumes of liquid from the pipette.

Various changes and modifications may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be embraced by the annexed claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

l. A measuring pipette for liquids, comprising a graduated tubular member open at top and bottom and provided with a laterally projecting branch communicating with the interior of said member, a suction valve normally closing said branch to permit the flow of liquid into said member, a discharge valve normally closing said open bottom of said member to permit dispensing of liquid from said member, spaced upper and lower locking rings ring and at least one of said locking rings, a piston extending into said member through said open top and having an enlarged end, a collar arranged about said piston adjacent said enlarged end, frame means connecting said collar with said base ring, and means removably securing said collar to said piston, whereby upon movement of said base ring for abutment against said upper locking ring a predetermined volume of liquid is sucked into said member through said suction valve, while upon reverse movement of said base ring discharge of said liquid takes place through said discharge valve, said volume being'variable by adjusting said means for securing said locking rings and said collar relative to said member and said piston, respectively.

2. A pipette according to claim 1, said spring means extending between said lower locking ring and said base ring, whereby upon release of said base ring liquid will be automatically sucked into said member.

3. A pipette according to claim 1, said spring means extending between said upper locking ring and said baseing said rings to said member in selected positions along said member, a base ring slidably mounted on said member for movement between said locking rings, means rigidly interconnecting said base ring and said piston for conjoint movement, and spring means abutting at one end thereof against said base ring and the other end thereof abutting against one of said locking rings for urging said piston outwardly of said tubular member.

5. A pipette as in claim 4, wherein the locking ring adjacent the discharge end of said tubular member includes laterally projecting finger stalls, and said spring means abuts said last mentioned locking ring at the other end thereof.

6. A pipette comprising a tubular member having an open upper end and a lower discharge end, a piston slidably mounted in said tubular member with the upper end of said piston projecting outwardly of the open end of said tubular member, abutment means arranged for conjoint movement with said piston, abutment means mounted on said tubular member, each of said abutment means being engageable with the other abutment means for limiting the relative movement between piston and tubular member, one of said abutment means being slidably movable to selected positions along the longitudinal extent of said tubular member and piston, and means for fixing the position of said one abutment means relative to the longitudinal extent of said tubular member and piston, and spring means arranged exteriorly of said tubular member for urging said piston outwardly of said tubular member.

References Cited in the file of this patent UNlTED STATES PATENTS 2,198,666 Gruskin Apr. 30, 1940 2,205,875 Coffey et al June 25, 1940' 2,521,433 White Sept. 5, 1950 FOREIGN PATENTS 16,069 Great Britain 1909 

